On 2011-02-03, mm wrote:
U-haul says for ttrailer rental:

Must be equipped with a hard top if it is an SUV or Jeep. U-Haul does
not allow any type of sport-utility vehicle not equipped with a hard
top to tow U-Haul equipment.

How come?

Maybe they want to avoid being sued in the event of an accident where
the trailer gets smashed into the vehicle and mushes somebody?

Just a guess.